Can you open the Chrome developer tools and go to the network tab when you try to paste an image in? Do you see anything red there off hand? Would it be possible to screenshot the contents of that tab?
I believe it to be a potential error in our content-security-policy string in .htaccess and NOT a XenForo bug. Therefore this bug is most likely not a bug - but a configuration error. The string we use is very long and complex, and probably not for a very good reason. All is well and thanks for your suggestions. Basic debugging would have resolved the problem - time constraints prevented this. Thank you.